Electrodepositable compositions containing sulfonium resins and capped polyisocyanates

ABSTRACT

It has been found that aqueous coating compositions comprising a blocked organic polyisocyanate and quaternary sulfonium group-containing resin containing isocyanate reactive groups can be electrodeposited. These compositions deposit on the cathode to provide coatings having excellent properties including solvent resistance, salt spray and detergent resistance, hardness, flexibility, and most importantly a resistance to yellowing, especially when used to formulate white or pastel coatings.

This is a continuation of application Ser. No. 316,596, filed Dec. 19,1972, now abandoned.

BACKGROUND OF THE INVENTION

Electrodeposition as a coating application method involves thedeposition of a film-forming material under the influence of an appliedelectrical potential and has become of increasing commercial importance.Along with the increased use of such methods has been the development ofvarious compositions which provide more or less satisfactory coatingswhen applied in this manner. However, most conventional coatingtechniques do not produce commercially usable coatings, andelectrodeposition of many coating materials, even when otherwisesuccessful, is often attended by various disadvantages such asnon-uniform coatings and by poor throw power, i.e., the ability to coatareas of the electrode which are remote or shielded from the otherelectrode. In addition, the coatings obtained are in many instancesdeficient in certain properties essential for the utilization in certainapplications for which electrodeposition is otherwise suited. Inparticular, properties such as corrosion resistance and alkaliresistance are difficult to achieve with the resins conventionallyemployed in electrodeposition processes, and many electrodepositedcoatings are subject to discoloration or staining because of chemicalchanges associated with electrolytic phenomena at the electrodes andwith the types of resinous materials ordinarily utilized. This isespecially true with the conventional resin vehicles used inelectrodeposition processes which contain polycarboxylic acid resinsneutralized with a base; these deposit on the anode and because of theiracidic nature tend to be sensitive to common types of corrosive attack,e.g., by salt, alkali, etc. Further anodic deposition tends to place theuncured coating in proximity to metal ions evolved at the anode, therebycausing staining with many coating systems.

The preparation of white or pastel films with high gloss, glossretention, and resistance to yellowing is a particular problem inelectrodepositable films.

DESCRIPTION OF THE INVENTION

It has now been found that aqueous compositions comprising a capped orblocked organic polyisocyanate and a quaternary sulfoniumgroup-containing resin may be electrodeposited on a cathode to producecoatings with highly desirable properties, including alkali resistance,resistance to staining, and resistance to yellowing.

The capped or blocked isocyanate which may be employed in thecompositions of the invention may be any isocyanate where the isocyanatogroups have been reacted with a compound so that the resultant cappedisocyanate is stable to hydroxyl groups at room temperature but reactivewith hydroxy and/or epoxy groups at elevated temperatures, usuallybetween about 200° F. and about 600° F.

In the preparation of the blocked organic polyisocyanate, any suitableorganic polyisocyanate may be used. Representative examples are thealiphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine, and butylidene diisocyanates;the cycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane,and 1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates; the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; the nuclear substitutedaromatic compounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate, and chloro-diphenylene diisocyanate; the triisocyanatessuch as triphenyl methane-4,4',4"-triisocyanate, 1,3,5-triisocyanatebenzene, and 2,4,6-triisocyanate toluene; and the tetra-isocyanates suchas 4,4'-diphenyl-dimethyl methane- 2,2'-5,5'-tetraisocyanate; thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate terminated prepolymers may be simple polyols such as glycols,e.g., ethylene glycol and propylene glycol, as well as other polyolssuch as glycerol, trimethylolpropane, hexanetriol, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide, and the like. These are generally calledhydroxy-terminated polyethers and can be linear or branched. Examples ofpolyethers include polyoxyethylene glycol having a molecular weight of1540, polyoxypropylene glycol having a molecular weight of 1025,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol, and mixtures thereof. Other types ofpolyoxyalklene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose, and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

Any suitable aliphatic aliphatic, cycloaliphatic, or aromatic alkylmonoalcohol may be used as a blocking agent in accordance with thepresent invention, such as, for example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexanol, decyl, and lauryl alcohols, and the like;the cycloaliphatic alcohols such as, for example, cyclopentanol,cyclohexanol, and the like, the aromatic-alkyl alcohols, such as,phenylcarbinol, methylphenylcarbinol, and the like. Minor amounts ofeven higher molecular weight relatively non-volatile monoalcohols may beused, if desired, to serve as plasticizers in the coatings provided bythis invention.

Additional blocking agents include hydroxyl amines such as ethanolamineand oximes such as methylethyl ketone oxime, acetone oxime, andcyclohexanone oxime.

The organic polyisocyanate-blocking agent adduct is formed by reacting asufficient quantity of alcohol with the organic polyisocyanate to insurethat no free isocyanate groups are present. The reaction between theorganic polyisocyanate and the blocking agent is exothermic; therefore,the polyisocyanate and the blocking agent are preferably admixed attemperatures no higher than 80° C. and, preferably, below 50° C. tominimize the exotherm effect.

As previously stated, the composition employed in the method of thisinvention is a coating composition comprising an aqueous dispersionprepared from a fully capped or blocked organic polyisocyanate with aresin solubilized through a quaternary sulfonium salt group.

Electrodepositable compositions, while referred to as "solubilized", infact are considered a complex solution, dispersion or suspension, orcombination of one or more of these classes in water which acts as anelectrolyte under the influence of an electric current. While, no doubtin some circumstances the vehicle resin is in solution, it is clear thatin some instances, and perhaps in most, the vehicle resin is adispersion which may be called a molecular dispersion of molecular sizebetween a colloidal suspension and true solution.

The sulfonium group-containing resins employed in the compositions ofthis invention are ungelled, water-dispersable, epoxy resins having intheir molecule at least one 1,2-epoxy group per average molecule andcontaining chemically-bound quaternary sulfonium base salts, thequaternary sulfonium base salts preferably being salts of boric acidand/or an acid having a dissociation constant greater than boric acid,including organic and inorganic acids. Upon solubilization, at least aportion of the salt is preferably a salt of an acid having adissociation constant greater than about 1 × 10.sup.⁻⁵ and especiallywhere the resin is oxyalkylene group free. Preferably, the acid is anorganic, carboxylic acid. The presently preferred acid is lactic acid.Preferably the resin contains from about 0.1 to about 35 percent byweight sulfur and at least about 1 percent of said sulfur and preferablyabout 20 percent, more preferably about 50 percent, and most preferably,substantially all of the sulfur being in the form of chemically-boundquaternary sulfonium base salt groups.

The resins within the purview of this invention thus include (a) epoxygroup-containing resins containing, in addition, quaternary sulfoniumgroups which resins may or may not contain chemically-bound boron orwhich may be dispersed for electrocoating with or without the additionof a boron compound and especially boric acid or a precursor thereof; or(b) epoxy group-containing resins containing, in addition, quaternarysulfonium base salts of an acid having a dissociation constant greaterthan 1 × 10.sup.⁻⁵, which resin may or may not contain chemically-boundboron or which resin may be dispersed for electrocoating with or withoutthe addition of a boron compound, and especially boric acid or aprecursor thereof.

The epoxy compound can be any monomeric or polymeric compound or mixtureof compounds having a 1,2-epoxy equivalency greater than 1.0, that is,in which the average number of 1,2-epoxy groups per molecule is greaterthan 1. It is preferred that the epoxy compound be resinous, that is, apolyepoxide, i.e., containing more than one epoxy group per moleculeand, preferably, containing free hydroxyl groups. The polyepoxide can beany of the well-known epoxides. Examples of these polyepoxides have, forexample, been described in U.S. Pat. Nos. 2,467,171; 2,615,007;2,716,123; 3,030,336; 3,053,855; and 3,075,999. A useful class ofpolyepoxides are the polyglycidyl ethers of polyphenols, such asBisphenol A. These may be produced, for example, by etherification of apolyphenol with epichlorohydrin or dichlorohydrin in the presence of analkali. The phenolic compound may be bis(4-hydroxyphenyl)-2,2-propane,3,4'-dihydroxybenzophenone, bis(4-hydroxyphenol)- 1,1-ethane,bis(4-hydroxyphenyl) 1,1-isobutane;bis(4-hydroxytertiary-butylphenyl)2,2-propane,bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthaline, or the like.Another quite useful class of polyepoxides are produced similarly fromnovolak resins or similar polyphenol resins.

Also suitable are the similar polyglycidyl ethers of polyhydric alcoholswhich may be derived from such polyhydric alcohols as ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propylene glycol,1,4-butylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol,bis(4-hydroxycyclohexyl)2,2-propane, and the like.

There can also be used polyglycidyl esters of polycarboxylic acids whichare produced by the reaction of epichlorohydrin or a similar epoxycompound with an aliphatic or aromatic polycarboxylic acid, such asoxalic acid, succinic acid, glutaric acid, terephthalic acid,2,6-naphthylene dicarboxylic acid, dimerized linolenic acid, and thelike. Examples are diglycidyl adipate and diglycidyl phthalate.

Also useful are polyepoxides derived from the epoxidation of anolefinically unsaturated alicyclic compound. Included are diepoxidescomprising in part one or more monoepoxides. These polyepoxides arenonphenolic and are obtained by epoxidation of alicyclic olefins, forexample, by oxygen and selected metal catalysts, by perbenzoic acid, byacetaldehyde monoperacetate, or by peracetic acid. Among suchpolyepoxides are the epoxyalicyclic ethers and esters, which are wellknown in the art.

Another class of polyepoxides are those containing oxyalkylene groups inthe epoxy molecule. Such oxyalkylene groups are typically groups of thegeneral formula: ##STR1## where R is hydrogen or alkyl, preferably loweralkyl (e.g., having 1 to 6 carbon atoms), and where, in most instances,m is 1 to 4 and n is 2 to 50. Such groups can be pendent to the mainmolecular chain of the polyepoxide or part of the main chain itself. Theproportion of oxyalkylene groups in the polyepoxide depends upon manyfactors, including the chain length of the oxyalkylene group, the natureof the epoxy, and the degree of water solubility desired. Usually theepoxy contains at least about 1 percent by weight or more, andpreferably 5 percent or more, of oxyalkylene groups.

Some polyepoxides containing oxyalkylene groups are produced by reactingsome of the epoxy groups of a polyepoxide, such as the epoxy resinsmentioned above, with a monohydric alcohol containing oxyalkylenegroups. Such monohydric alcohols are conveniently produced byoxyalkylating an alcohol, such as methanol, ethanol, or other alkanol,with an alkylene oxide. Ethylene oxide, 1,2-propylene oxide, and1,2-butylene oxide are especially useful alkylene oxides. Othermonohydric alcohols can be, for example, the commercially-availablematerials known as Cellosolves and Carbitols, which are monoalkyl ethersof polyalkylene glycols. The reaction of the monohydric alcohol and thepolyepoxide is generally carried out in the presence of a catalyst.Formic acid, dimethylethanolamine, diethylethanolamine,N,N-dimethylbenzylamine, and, in some cases, stannous chloride, areuseful for this purpose.

Similar polyepoxides containing oxyalkylene groups can be produced byoxyalkylating the epoxy resin by other means, such as by direct reactionwith an alkylene oxide.

The polyepoxide employed to produce the foregoing epoxies containingoxyalkylene groups should contain a sufficient number of epoxy groups sothat the average number of residual epoxy groups per molecule remainingin the product after the oxyalkylation is greater than 1.0. Whereoxyalkylene groups are present, the epoxy resin preferably contains fromabout 1.0 to about 90 percent or more by weight of oxyalkylene groups.

These epoxides which tend to contain unreacted alcohols orhydroxyl-containing by-products are presently less preferred unlesspurified to remove interfering hydroxyl-containing materials.

Other epoxy-containing compounds and resins include nitrogeneousdiepoxides such as disclosed in U.S. Pat. No. 3,365,471; epoxy resinsfrom 1,1-methylene bis(5-substituted hydantoin), U.S. Pat. No.3,391,097; bis-imide containing diepoxides, U.S. Pat. No. 3,450,711;epoxylated aminomethyldiphenyl oxides, U.S. Pat. No. 3,312,664;heterocyclic N,N'-diglycidyl compounds, U.S. Pat. No. 3,503,979; aminoepoxy phosphonates, British Pat. No. 1,172,916; 1,3,5-triglycidylisocyanurates, as well as other epoxy-containing materials known in theart.

The presently preferred class of resins which may be employed areacrylic polymers containing epoxy groups and hydroxyl groups. Preferablythese acrylic polymers are polymers formed by copolymerizing anunsaturated epoxy-containing monomer, such as, for example, glycidylacrylate or methacrylate, a hydroxyl containing unsaturated monomer, andat least one other unsaturated monomer.

Any polymerizable monomeric compound containing at least one CH₂ =C<group, preferably in terminal position, may be polymerized with theunsaturated glycidyl compounds. Examples of such monomers include:

1. Monoolefinic and diolefinic hydrocarbons, that is, monomerscontaining only atoms of hydrogen and carbon, such as styrene,alpha-methyl styrene, alpha-ethyl styrene, isobutylene (2-methylpropene-1), 2-methyl-butene-1, 2-methyl-pentene-1,2,3-dimethyl-butene-1, 2,3-dimethyl-pentene-1, 2,4-dimethyl-pentene-1,2,3,3-trimethylbutene-1, 2-methyl-heptene-1, 2,3-dimethyl-hexene-1,2,4-dimethyl-hexene-1, 2,5-dimethyl-hexene-1,2-methyl-3-ethyl-pentene-1, 2,3,3-trimethyl-pentene-1,2,3,4-trimethyl-pentene-1, 2-methyl-octene-1, 2,6-dimethyl-heptene-1,2,6-dimethyl-octene-1, 2,3-dimethyl-decene-1, 2-methyl-nonadecene-1,ethylene, propylene, butylene, amylene, hexylene, butadiene-1,3,isopropene, and the like;

2. Halogenated monoolefinic and diolefinic hydrocarbons, that is,monomers containing carbon, hydrogen, and one or more halogen atoms,such as alpha-chlorostyrene, alpha-bromostyrene, 2,5-dichlorostyrene,2,5-dibromostyrene, 3,4-dichlorostyrene, ortho-, meta-, andpara-fluorostyrenes, 2,6-dichlorostyrene, 2,6-difluorostyrene,3-fluoro-4-chlorostyrene, 3-chloro-4-fluorostyrene,2,4,5-trichlorostyrene, dichloromonofluorostyrenes, 2-chloropropene,2-chlorobutene, 2-chloropentene, 2-chlorohexene, 2-chloroheptene,2-bromobutene, 2-bromoheptene, 2-fluorohexene, 2-flurobutene,2-iodoprene, 2-iodopentene, 4-bromoheptene, 4-chloroheptene,4-fluoroheptene, cis- and trans-1,2-dichloroethylene,1,2-dibromoethylene, 1,2-difluroethylene, 1,2-diiodoethylene,chloroethylene (vinyl chloride), 1,1-dichloroethylene (vinylidenechloride), bromoethylene, fluoroethylene, iodoethylene,1,1-dibromoethylene, 1,1-fluoroethylene, 1,1-diiodoethylene,1,1,2,2-tetrafluoroethylene, 1-chloro-2,2,2-trifluoroethylene,chlorobutadiene, and other halogenated diolefinic compounds;

3. Esters of organic and inorganic acids, such as vinyl acetate, vinylpropionate, vinyl butyrate, vinyl isobutyrate, vinyl valarate, vinylcaproate, vinyl enanthate, vinyl benzoate, vinyl toluate, vinylp-chlorobenzoate, vinyl-o-chlorobenzoate, and similar vinylhalobenzoates, vinyl-p-methoxybenzoate, vinyl-o-methoxybenzoate,vinyl-p-ethoxybenzoate, methyl methacrylate, ethyl methacrylate, propylmethacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate,heptyl methacrylate, octyl methacrylate, decyl methacrylate, methylcrotonate, and ethyl tiglate;

Methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,butyl acrylate, isobutyl acrylate, amyl acrylate, hexyl acrylate,2-ethylhexyl acrylate, heptyl acrylate, octyl acrylate,3,5,5-trimethylhexyl acrylate, decyl acrylate, and dodecyl acrylate;

Isopropenyl acetate, isopropenyl propionate, isopropenyl butyrate,isopropenyl isobutyrate, isopropenyl valerate, isopropenyl caproate,isopropenyl enanthate, isopropenyl benzoate, isopropenylp-chlorobenzoate, isopropenyl o-chlorobenzoate, isopropenylo-bromobenzoate, isopropenyl m-chlorobenzoate, isopropenyl toluate,isopropenyl alpha-chloroacetate, and isopropenyl alpha-bromopropionate;

Vinyl alpha-chloroacetate, vinyl alpha-bromoacetate, vinylalpha-chloropropionate, vinyl alpha-bromopropionate, vinylalpha-iodopropionate, vinyl alpha-chlorobutyrate, vinylalpha-chlorovalerate, and vinyl alpha-bromovalerate;

Allyl chloride, allyl cyanide, allyl bromide, allyl fluoride, allyliodide, allyl chlorocarbonate, allyl nitrate, allyl thiocyanate, allylformate, allyl acetate, allyl propionate, allyl butyrate, allylvalerate, allyl caproate, allyl-3,5,5-trimethyl hexoate, allyl benzoate,allyl acrylate, allyl crotonate, allyl oleate, allyl chloroacetate,allyl trichloroacetate, allyl chloropropionate, allyl chlorovalerate,allyl lactate, allyl pyruvate, allyl aminoacetate, allyl acetoacetate,allyl thioacetate, as well as methallyl esters corresponding to theabove allyl esters, as well as esters from such alkenyl alcohols asbeta-ethyl allyl alcohol, beta-propyl allyl alcohols, 1-butene-4-ol,2-methyl-butene-4-ol, 2(2,2-dimethylpropyl)-1-butene-4-ol, and1-pentene-4-ol;

Methyl alpha-chloroacrylate, methyl alpha-bromoacrylate, methylalpha-fluoroacrylate, methyl alpha-iodoacrylate ethyl alpha,chloroacrylate, propyl alpha-chloroacrylate, isopropylalpha-bromoacrylate, amyl alpha-chloroacrylate, octylalpha-chloroacrylate, 3,5,5-trimethylhexyl alpha-chloroacrylate, decylalpha-chloroacrylate, methyl alpha-cyanoacrylate, ethylalpha-cyanoacrylate, amyl alpha-cyanoacrylate, and decylalpha-cyanoacrylate.

Dimethyl maleate, diethyl maleate, diallyl maleate, dimethyl fumarate,diethyl fumarate, dimethallyl fumarate, and diethyl glutaconate;

Organic nitriles such as acrylonitrile, methacrylonitrile,ethacrylonitrile, 3-octenenitrile, crotonitrile, oleonitrile, and thelike.

In carrying out the polymerization reaction, techniques well known inthe art may be employed. A peroxygen type catalyst is ordinarilyutilized. Diazo compounds or redox catalyst systems can also be employedas catalysts.

The preferred hydroxy-containing unsaturated monomers are hydroxyalkylacrylates, for example, hydroxyethyl acrylate or methacrylate,hydroxypropyl acrylate or methacrylate.

Another method of producing acrylic polymers which may be utilized inthis invention is to react an acrylic polymer containing reactive sites,including hydroxy groups, with an epoxy-containing compound such as thediglycidyl ether of Bisphenol A or other polyepoxides as enumeratedelsewhere herein, to provide an epoxy group-containing hydroxyl groupcontaining acrylic polymer.

The resins of the invention are formed by reacting the epoxy compoundwith a sulfide in the presence of an acid to form quaternary sulfoniumbase group-containing resins.

The sulfide employed may be virtually any sulfide which reacts withepoxy groups and which does not contain interfering groups. For example,the sulfide may be aliphatic, mixed aliphatic-aromatic, aralkyl, orcyclic. Examples of such sulfides include diethyl sulfide, dipropylsulfide, dibutyl sulfide, diphenyl sulfide, dihexyl sulfide, ethylphenyl sulfide, tetramethylene sulfide, pentamethylene sulfide,thiodiethanol, thiodipropanol, thiodibutanol, and the like.

The acid employed may be virtually any acid which forms a quaternarysulfonium salt. Preferably the acid is an organic carboxylic acid.Examples of acids which may be employed are boric acid, formic acid,lactic acid, acetic acid, propionic acid, butyric acid, hydrochloricacid, phosphoric acid, and sulfuric acid. Preferably, the acid is anacid having a dissociation constant greater than about 1 × 10⁻ ⁵.

The ratio of sulfide to acid is not unduly critical. Since one mole ofacid is utilized to form one mole of sulfonium group, it is preferredthat at least about one mole of acid be present for each mole of desiredsulfide to sulfonium conversion.

The sulfide/acid mixture and the epoxy compound are reacted by mixingthe components, usually at moderately elevated temperatures such as70°-110° C. A solvent is not necessary, although one is often used inorder to afford better control of the reaction. Aromatic hydrocarbons,monoalkyl ethers of ethylene glycol, aliphatic alcohols are suitablesolvents. The proportions of the sulfide and the epoxy compound can bevaried, and the optimum proportions depend upon the particularreactants. Sufficient sulfide should be utilized to provide sufficientquaternary sulfonium groups to solubilize the resin. Ordinarily,however, from about 1 part to about 50 parts by weight of the sulfideper 100 parts of epoxy compound is employed. The proportions are usuallychosen with reference to the amount of sulfur, which is typically fromabout 0.1 to about 35 percent, based on the total weight of the sulfideand the epoxy compound. Since the sulfide salt reacts with the epoxidegroups of the epoxy resin employed, in order to provide an epoxygroup-containing resin, less of the sulfide than the stoichiometricequivalent of the epoxide groups present is utilized so that the finalresin is provided with one epoxy group per average molecule. Whenepoxy-free resins are desired, the stoichiometry is adjusted to reactall the epoxy groups, or the remaining epoxy groups are hydrolyzed orotherwise reacted.

Where it is desired to incorporate boron into the resin molecule, onemethod is to incorporate boron by means of an amine borate ornitrogen-containing boron ester as described in copending ApplicationSer. No. 100,825, filed Dec. 22, 1970, the disclosure of which is herebyincorporated by reference. The boron compound reacts with availableepoxy groups to provide quarternary ammonium borate groups in the resinmolecule.

The reaction of the boron compound may be conducted simultaneously withsulfonium group formation since the reaction conditions for thisreaction are similar.

The particular reactants, proportions, and reaction conditions should bechosen in accordance with considerations well known in the art so as toavoid gellation of the product during the reaction. For example,excessively severe reaction conditions should not be employed.Similarly, compounds having reactive substituents should not be utilizedalong with epoxy compounds with which those substituents might reactadversely at the desired conditions.

The product forming the resin of the invention may be crosslinked tosome extent; however, it remains soluble in certain organic solvents andcan be further cured to a hard, thermoset state. It is significantlycharacterized by its epoxy content and chemically-bound quaternarysulfonium content.

Aqueous compositions containing the above reaction products are highlyuseful as coating compositions and can be applied by any conventionalmethod, such as by dipping, brushing, etc. They are, however, eminentlysuited to application by electrodeposition.

The resins of the invention are water-dispersible per se; however,additional acid solubilizing agents may be added if desired.

When epoxy groups are present in the final resin, the presence of aboron compound in the electrodeposited film is of substantial benefit inthat boron compounds apparently catalyze the cure of the deposited film,allowing lower cure temperatures and/or harder films. Where the resin isfirst prepared without the presence of boron and/or additional boron isdesired when the resin is dispersed, a compound of boron may be added,preferably boric acid or a precursor thereof.

The acid or acidic solubilizing agent is preferably any acid having adissociation constant greater than 1 × 10⁻ ⁵. Preferably, the acid oracidic solubilizing agent should be an organic acid having adissociation constant greater than about 1 × 10⁻ ⁵, the presentlypreferred acid being lactic acid. The addition of acid aids instabilizing the resin since the epoxy may tend to further polymerize onstorage under highly alkaline conditions. In some cases the acid alsohelps to obtain more complete dissolution of the resin. It is alsodesirable to electrodeposit these coatings from an acidic or onlyslightly basic solution (e.g., having a pH between about 3 and about8.5), and the addition of acid thus is often useful to achieve thedesired pH.

The resin of the invention, when placed in a water-containing mediumsuch as an electrodeposition, high solids feed concentrate or theelectrodeposition bath, changes character. Since frequently the boron,if present and chemically bonded, is apparently weakly chemically-boundin the resin, it is subject to cleavage from the resin molecule and,while the boron electrodeposits with the resin and is found in theelectrodeposited film, the boron may be removed from thewater-containing medium in whole or in part by separation means such aselectrodialysis or ultrafiltration in the form of boric acid.

Thus, the resin in aqueous medium can be characterized as a solubilizedresin having chemically-bound quaternary sulfonium base salts andcontaining active crosslinking sites such as active hydrogens,preferably hydroxyl and/or epoxy groups.

The resin contains from about 0.1 to about 35 percent by weight sulfur,at least about 1 percent of said sulfur and preferably about 20 percentmore preferably 50 percent and most preferably substantially all, of thesulfur being in the form of chemically-bound quarternary sulfonium basesalt groups.

These sulfonium group-containing resins are disclosed in copendingapplications Ser. No. 217,278, now abandoned filed Jan. 12, 1972, andSer. No. 292,360, filed Sept. 26, 1972 and now abandoned. Theseelectrodepositable resins, while referred to as "solubilized", in factare considered a complex solution, dispersion, or suspension, orcombination of one or more of these classes in water, which acts as anelectrolyte under the influence of an electric current, while, no doubt,in some instances, or perhaps in most, the resin is a dispersion whichmay be called a molecular dispersion of molecular size between acolloidal suspension and a true solution.

The polyisocyanate-blocking agent adduct is preferably admixed with thecompound containing sulfonium base salt groups in ratios of from about0.5 to about 2.0 urethane groups for each reactive/crosslinking site,preferably hydroxyl groups.

The capped isocyanate-quaternary sulfonic resin mixture iselectrodeposited on a suitable substrate and cured at elevatedtemperatures such as from about about 250° F. to about 600° F. At thesehigher temperatures the reactivity of the hydroxyl group, epoxy group,or other crosslinking site is such to enable it to break the urethanelink of the adduct and react with the freed NCO groups to form asubstituted urea. The alcohol released may either volatilize or remainin the mixture as a plasticizer, depending essentially on its boilingpoint.

Aqueous compositions containing the above components are highly usefulas coating compositions particularly suited to application byelectrodeposition. It is not always necessary to add a neutralizingagent to the product in order to obtain a suitable aqueous composition,although an acid or acidic neutralizing agent is more preferably added.It is desirable to electrodeposit these coatings from a solution havinga pH between 3 and about 9. The addition of acid thus is often useful toachieve the desired pH.

The concentration of the product in water depends upon the processparameters to be used and is in general not critical, but ordinarily themajor proportion of the aqueous composition is water, e.g., thecomposition may contain 1 to 25 percent by weight of the resin. In mostinstances a pigment composition and, if desired, various additives suchas anti-oxidants, surface-active agents, and the like are included. Thepigment composition may be of any conventional type comprising, forexample, one or more pigments such as iron oxides, lead oxides,strontium chromate, carbon black, titanium dioxide, talc, bariumsulfate, cadmium yellow, cadmium red, chromic yellow, and the like.

In electrodeposition processes employing the aqueous coatingcompositions described above, the aqueous composition is placed incontact with an electrically conductive anode and an electricallyconductive cathode, with the surface to be coated being the cathode.Upon passage of electric current between the anode and the cathode,while in contact with the bath containing the coating composition, anadherent film of the coating composition is deposited on the cathode.This is in contrast to processes utilizing polycarboxylic acid resinswhich deposit on the anode, and many of the advantages described aboveare in large part attributed to this cathodic deposition.

The conditions under which the electrodeposition is carried out are ingeneral similar to those used in electrodeposition of other types ofcoatings. The applied voltage may be varied greatly and can be, forexample, as low as one volt or as high as several thousand volts,although typically between 50 volts and 500 volts. The current densityis usually between about 1.0 ampere and 15 amperes per square foot andtends to decrease during electrodeposition.

The method of the invention is applicable to the coating of anyelectrically conductive substrate, and especially metals such as steel,aluminum, copper, or the like.

After deposition, the coating is cured at elevated temperatures by anyconvenient method such as in baking ovens or with banks of infrared heatlamps. Curing temperatures are preferably from about 350° F. to about425° F., although curing temperatures from about 250° F. to about 500°F., or even 600° F., may be employed if desired.

Illustrating the invention are the following examples which, however,are not construed as limiting the invention to their details. All partsand percentages in the examples, as well as throughout thisspecification, are by weight unless otherwise specified.

EXAMPLE I

The following sample illustrates the preparation of a quaternarysulfonium salt-solubilized acrylic resin in an electrodepositablecomposition containing a blocked organic polyisocyanate resin incombination therewith. The acrylic resin was prepared as follows: Themonomer feed compostion was as follows: t1 -Monomer? Parts by Weight?-Methyl methacrylate 1300 -Ethyl acrylate 1060 -Hydroxyethyl acrylate600 -Styrene 600 -Glycidyl methacrylate 440 -

The above monomer mixture also contained 60 parts of Vazo[azo-bis(isobutyronitrile)] and 120 parts of tertiary dodecyl mercaptan.

The polymer was prepared in the reaction flask equipped with athermometer, stirrer, reflux condenser, monomer addition means and acontinuous nitrogen gas blanket.

Into the reactor were charged 1000 parts of n-butyl Cellosolve. Thecontents of the reactor were heated to 90° C. with agitation under anitrogen blanket. One-quarter of the total of the monomers containinginitiator and mercaptan were added over a period of 25 minutes. Duringthis time an exotherm was noted and the temperature increased to 120° C.After an additional 25 minutes, the temperature dropped to 114° C. andthere was added, over a 41/2 hour period, the remaining monomercomposition. At the end of the addition, the temperature had risen to143° C. and the reaction mixture was held between 130°-140° C. for anadditional 4 hours. The reaction mixture was then cooled and there wasadded 4 parts of 2,6-ditertiarybutyl paracresol.

The above reaction mixture was then cooled to 93° C. and there was thenadded a mixture comprising 378 parts of thiodiethanol, 328 parts of 85percent lactic acid solution in water and 300 parts of deionized water.This addition was made over a 2-minute period. The temperature of thereaction mixture dropped to 80° C. The reaction mixture was heated tobetween 97° C. and 101° C. for 45 minutes and there was then added 200parts of deionized water.

The analysis of the final resin showed 71.3 percent solids, a hydroxylvalue of 176 and an epoxy value of infinity. The product had a viscosityof 54,000 centipoises. This product is identified as Polymer A.

A pigment paste was formed by admixing 210 parts of Polymer A with 600parts of titanium dioxide, 6 parts of a cationic surfactant (AerosolC-61) and 75 parts of butyl Cellosolve. This mixture was ground in alaboratory sand mill for 25 minutes. There was then added an additional55 parts of butyl Cellosolve.

An electrodepositable composition was then formulated as follows: Therewere admixed 35.3 parts of the above pigment paste, 51.6 parts ofPolymer A and 9.4 parts (7.5 parts of solids) of a 2-ethylhexanol cappedtrifunctional aliphatic isocyanate (Desmodur N-100), the solvent presentbeing methyl-n-butyl ketone, 1.0 part dibutyl tin dilaurate and 625parts of deionized water. This provided an approximately 10 percentsolids electrodepositable composition.

The above composition was electrodeposited on zinc phosphate steelpanels at 300 volts for 120 seconds at a bath temperature of 77° F. Theresultant electrodeposited film was baked at 350° F. for 25 minutes. Thefilm build was 1.25 mils, the film had a 2H+ pencil hardness andwithstood 80 inch pounds direct impact and showed a slight failure at 80inch pounds reverse impact. The panel was highly resistant to acetonerubbing.

Calcium zinc phosphate treated steel panels were electrocoated undersimilar conditions and showed a 60° gloss reading of 82-84.

Salt spray panels similarly electrocoated passed an excess of 312 hourssalt spray.

EXAMPLE II

In a manner similar to Example I, the following was prepared from amonomer feed of the following composition:

    ______________________________________                                        Monomer             Parts by Weight                                           ______________________________________                                        Ethyl acrylate      2100                                                      Methyl methacrylate 1800                                                      Glycidyl methacrylate                                                                             900                                                       2-hydroxyethyl acrylate                                                                           900                                                       Styrene             300                                                       ______________________________________                                         The above monomer mixture also contained 180 parts of tertiary dodecyl     mercaptan and 90 parts of Vazo [azo-bis(isobutyronitrile)].

After the polymerization was complete, there was added to the resultantpolymer 6 parts of 2,6-ditertiarybutyl paracresol.

To the above polymer at 93° C. there was added a mixture of 370 parts ofthiodiethanol, 318 parts of 85 percent lactic acid and 300 parts ofdeionized water. This mixture was added over a 2-minute period. Thetemperature of the mixture dropped to 84° C. and the mixture was heated,with stirring, to 98° C. for 80 minutes, at which time an additional 360parts of water were added.

The analysis of the resultant polymer showed 72.5 percent solids, ahydroxyl value of 159 and an epoxy value of 5087, with a viscosity of46,800 centipoises. This polymer is hereinafter identified as Polymer B.

A pigment paste was prepared by admixing 212.2 parts of Polymer B, 196parts of titanium dioxide, 4 parts of pigmentary silica and 192 parts ofbutyl Cellosolve. The above mixture was ground in a Cowles mill to a 7+grind.

An electrodepositable composition was prepared by admixing 181.5 partsof Resin B, 130 parts of the above pigment paste and 32.4 parts of aketoxime blocked tri-functional aliphatic isocyanate (Desmodur N) (the32.4 parts of ketoxime comprising 25.9 parts solids dissolved inmethyl-n-butyl ketone. There was then added 2156 parts of deionizedwater to provide an approximately 10 percent solids electrodepositionbath having a pH of 7.7 and a conductivity of 290 mmhos. Zinc phosphatetreated steel panels were electrodeposited at 200 volts for 90 secondsat 77° F. and baked at 350° F. for 20 minutes. The resultant film buildwas one mil. The film had a 2H pencil hardness and withstood 160 inchpounds direct and reverse impact and had a 60° gloss of 72.

In a manner similar to the above examples, various other monomers asdescribed hereinabove can be utilized or prepared and theseinterpolymers can be reacted with other sulfide/acid combinations asdisclosed hereinabove to provide either epoxy containing or epoxy-freesulfonium salt group solubilized resins, which can be combined withvarious capped isocyanates as described above and electrodeposited orcoated in a conventional manner to provide highly useful coatingcompositions.

According to the provisions of the Patent Statutes, there are describedabove the invention and what are now considered to be its bestembodiments. However, within the scope of the appended claims, it is tobe understood that the invention can be practiced otherwise than asspecifically described.

We claim:
 1. An aqueous based resinous dispersion suitable for use as acoating composition comprising as the resinous phase:A. a quaternarysulfonium salt group solubilized synthetic organic resin containing freehydroxyl groups, said organic resin produced by reacting:
 1. anepoxy-containing organic material having a 1,2-epoxy equivalency ofgreater than 1, and2. a sulfide-acid mixture, said sulfide-acid mixturebeing used in an amount to provide sufficient quaternary sulfoniumgroups to solubilize said resin; said sulfide being selected from thegroup consisting of aliphatic, mixed aliphatic-aromatic, aralkyl andcyclic sulfides; and B. a capped, organic polyisocyanate stable atordinary room temperature in the presence of said resin (A) and reactivewith said resin (A) at elevated temperatures.
 2. The aqueous basedresinous dispersion as in claim 1 wherein (A) and (B) are present inproportions to provide about 0.5 to about 2.0 latent urethane groups perisocyanate reactive group.
 3. The aqueous based resinous dispersion asin claim 1 wherein the isocyanate reactive groups comprise hydroxylgroups.
 4. The aqueous based resinous dispersion as in claim 3 wherein(A) and (B) are present in proportions to provide about 0.5 to about 2.0latent urethane groups per hydroxyl group.
 5. The aqueous based resinousdispersion as in claim 1 wherein the resin (A) has a backbone derivedfrom the interpolymerization of an olefinically unsaturated glycidylcompound and at least one other copolymerizable olefinically unsaturatedmonomer.
 6. The aqueous based resinous dispersion as in claim 5 whereinthe resin (A) has a backbone derived from the interpolymerization of anolefinically unsaturated glycidyl compound, a hydroxyl alkyl ester ofacrylic or methacrylic acid, and at least one other copolymerizableolefinically unsaturated monomer.
 7. The aqueous based resinousdispersion as in claim 6 wherein (A) and (B) are present in proportionsto provide about 0.5 to about 2.0 latent urethane groups per hydroxylgroup.
 8. The aqueous based resinous dispersion as in claim 1 whereinthe resin (A) contains free epoxy groups.
 9. The aqueous based resinousdispersion as in claim 8 wherein (A) and (B) are present in proportionsto provide about 0.5 to about 2.0 latent urethane groups per isocyanatereactive group.
 10. The aqueous based resinous dispersion as in claim 8wherein the isocyanate reactive groups comprise hydroxyl groups.
 11. Theaqueous based resinous dispersion as in claim 10 wherein (A) and (B) arepresent in proportions to provide about 0.5 to about 2.0 latent urethanegroups per hydroxyl group.
 12. The aqueous based resinous dispersion asin claim 8 wherein the resin (A) has a backbone derived from theinterpolymerization of an olefinically unsaturated glycidyl compound andat least one other copolymerizable olefinically unsaturated monomer. 13.The aqueous based resinous dispersion as in claim 12 wherein the resin(A) has a backbone derived from the interpolymerization of anolefinically unsaturated glycidyl compound, a hydroxyl alkyl ester ofacrylic or methacrylic acid, and at least one other copolymerizableolefinically unsaturated monomer.
 14. The aqueous based resinousdispersion as in claim 13 wherein (A) and (B) are present in proportionsto provide about 0.5 to about 2.0 latent urethane groups per hydroxylgroup.